1. Field of the Invention
The present invention generally relates to an inspection method and apparatus of a glass substrate for imprint.
2. Description of the Related Art
Conventionally, as disclosed in Japanese patent publication No. 2008-68612, a nanoimprint mold is known. The nanoimprint mold includes a substrate, a pattern part with a concave-convex pattern formed on the substrate, a hard layer made of harder materials than the pattern part and formed on the surface of the pattern part, and a demolding layer formed on the surface of the hard layer. Each layer of the nanoimprint mold includes effective materials suitable for its respective role and lamination of the layers constitutes the nanoimprint mold. The nanoimprint mold is intended to be able to uniformly transfer an original pattern even to a flexible substrate, to prevent damage by pressure and contamination by resin, to enhance accuracy of a transferred pattern, and to improve durability.
The pattern part of the nanoimprint mold is constructed of flexible materials and is formed in a deformable state in order to be available for the flexible substrate. The hard layer of the nanoimprint mold is formed of an oxide film such as Si oxide (for example, SiO2) or ITO (i.e., Indium Tin Oxide) in order to enhance durability and accuracy of the transferred pattern. The demolding layer of the nanoimprint is formed of an organic molecular film to facilitate separation between polymer thin films on which nanoscale structures are impressed.
In addition, when an inspection to detect a pattern defect of the nanoimprint mold as disclosed in the Japanese patent publication No. 2008-68612, or an extraneous substance on a surface of a pattern part is performed, an inspection method by light is common. More specifically, a surface image of the nanoimprint mold is obtained by way of a dark-field light scattering method, and the pattern defect or the extraneous substance is detected.
However, the conventional inspection method by light has insufficient detection sensitivity for the nanoimprint mold disclosed in the Japanese patent publication No. 2008-68612. More specifically, in the inspection method by light, the detection sensitivity extremely decreases for the ultra fine pattern, and attachment of the extraneous substance or an organic substance whose size is less than 50 to 100 nm. Hence, the inspection method by light becomes difficult to apply to the minute scale objects. A major factor of this is considered to arise from the size of the pattern and the extraneous substance smaller than a wavelength of the light, which decreases a signal-to-noise (signal/noise) ratio.
As another inspection method, a defect inspection method by SEM (i.e., Scanning Electron Microscope) using a more sensitive electron beam than the light is possible. For example, the SEM inspection method makes it possible to use a smaller pixel size than the size of an inspection object by focusing the electron beam and to inspect the extraneous substance with high resolution. According to the SEM inspection method, the inspection of the nanoimprint mold disclosed in the Japanese patent publication No. 2008-68612 is possible. However, because of the small pixel size, the SEM inspection method needs an enormous amount of inspection time and the inspection in a practical time is difficult, which makes the SEM inspection method impractical. Moreover, when the nanoimprint mold is irradiated with the electron beam, charging becomes prominent and the appropriate pattern image cannot be obtained because the nanoimprint mold is entirely formed of insulation materials such as glass.